Vacuum pump

ABSTRACT

There is provided a vacuum pump capable of preventing foreign materials from flowing into a gap between rotors or the like and obtaining low ultimate pressure. The vacuum pump includes two rotating shafts formed extending in a first axial direction, a rotor casing, rotors, and a shielding portion. The rotor casing includes a rotor chamber disposed along the two rotating shafts, a suction port communicating with the rotor chamber, and an exhaust port communicating with the rotor chamber. The rotors are mounted on the two rotating shafts and disposed in the rotor chamber. The shielding portion is configured to prevent a gas sucked from the suction port into the rotor chamber from directly flowing into a gap between the rotors and is disposed between the suction port and inside the rotor chamber.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority to Japanese Application Nos. 2015-046274, filed Mar. 9, 2015 and 2016-018054, filed Feb. 2, 2016, the entire contents of which are hereby incorporated by reference.

TECHNICAL FIELD

The present invention relates to a vacuum pump.

BACKGROUND ART

In a fabrication process of a semiconductor device and a liquid crystal device, a dry vacuum pump is connected to a vacuum chamber to exhaust a process gas introduced into the vacuum chamber by the vacuum pump. The process gas to be exhausted by the vacuum pump may include a material solidified by reaction or the like inside the vacuum chamber or an easily solidified material mixed in as a foreign material.

The dry vacuum pump is designed to have a small gap (clearance) between a rotor and a rotor or between a rotor and a casing. Accordingly, when solidified materials enter inside the pump, the solidified materials may be deposited or trapped in a gap therebetween inside the pump, which may block rotor rotation. For this reason, a suction port of the dry vacuum pump may include a trap or a filter to prevent solidified materials from entering inside the pump.

[Patent Literature 1] Japanese Patent Laid-Open No. 5-332285.

SUMMARY OF INVENTION

When a process gas is prevented from entering the suction port of the dry vacuum pump, the ultimate pressure of the vacuum chamber connected to the dry vacuum pump will increase. Therefore, a trap or the like disposed in the suction port of the dry vacuum pump is configured to comprise a large trap or a plurality of stages of traps, and such a configuration causes an increase in size and cost of the fabrication apparatus. In addition, solidified materials deposited in the trap or the like causing clogging also prevent the dry vacuum pump from sucking the process gas, which may often require maintenance such as cleaning and replacement of the trap or the like.

In addition, as the dry vacuum pump, there have been known a screw type vacuum pump, a roots type vacuum pump, and a claw type vacuum pump. In general, the screw type vacuum pump is less affected by foreign materials than the roots type vacuum pump and the claw type vacuum pump. However, particularly in cases where light gases such as hydrogen are used as the process gas, the roots type vacuum pump and the claw type vacuum pump can have a lower ultimate pressure than the screw type vacuum pump.

In view of the above problems, an embodiment has been made, and an object of the embodiment is to provide a vacuum pump that can prevent foreign materials from entering into gaps such as between rotors and can have low ultimate pressure.

The vacuum pump of an embodiment includes two rotating shafts formed extending in a first axial direction; a rotor casing; rotors; and a shielding portion. The rotor casing includes a rotor chamber disposed along the two rotating shafts; a suction port communicating with the rotor chamber; and an exhaust port communicating with the rotor chamber. The rotors are mounted on the two rotating shafts and disposed in the rotor chamber. The shielding portion is configured to prevent a gas sucked from the suction port into the rotor chamber from directly flowing into a gap between the rotors and is disposed between the suction port and inside the rotor chamber.

According to this vacuum pump, the shielding portion is disposed between the suction port and inside the rotor chamber. This shielding portion prevents a gas sucked from the suction port into the rotor chamber from directly flowing into a gap between rotors. Thus, foreign materials can be prevented from being deposited or trapped in gaps between rotors.

In addition, the rotors may be roots type rotors or claw type rotors.

This configuration can achieve low ultimate pressure by the vacuum pump particularly in cases where light gases such as hydrogen are used as the process gas.

In addition, when viewed from the suction port toward inside the rotor chamber, the shielding portion may be disposed in front of a gap between the rotors.

This configuration can prevent foreign materials from directly flowing into the gap between the rotors.

In addition, the shielding portion may be disposed upstream of the rotors and may be disposed between the two rotating shafts when viewed from the suction port toward inside the rotor chamber.

This configuration can prevent foreign materials from directly flowing into the gap between the rotors.

In addition, the shielding portion may have a tapered shape narrow on an upstream side and wide on a downstream side. The shielding portion may also have a curved surface shape protruding toward upstream.

This configuration can effectively prevent foreign materials from directly flowing into the gap between the rotors.

In addition, the rotor chamber may comprise multistage rotor chambers connected to each other through a gas flow path. The rotors may comprise multistage rotors, each disposed in each of the multistage rotor chambers. The shielding portion may be disposed between the suction port and inside a first stage rotor chamber of the multistage rotor chambers.

This configuration can prevent foreign materials from directly flowing into the gap between the rotors inside the first stage rotor chamber.

In addition, the vacuum pump may further comprise a foreign material capture unit having at least one of a trap and a filter disposed in the gas flow path connecting between stages of the multistage rotor chambers.

This configuration allows the foreign material capture unit in the gas flow path to capture foreign materials contained in the gas. In addition, the foreign material capture unit for capturing foreign materials is disposed between stages of the multistage rotor chambers, and hence the foreign material capture unit does not prevent suction from the vacuum chamber to the first stage rotor chamber, whereby low ultimate pressure can be obtained. In addition, the foreign material capture unit is disposed downstream of the first stage rotor chamber whose pressure is greater than that of the suction port, thus allowing a simply configured foreign material capture unit to be used. Furthermore, even if foreign materials are deposited in the foreign material capture unit, this little affects the suction of the first stage rotor chamber, thus reducing frequency of maintenance of the foreign material capture unit.

In addition, the foreign material capture unit may be disposed in the gas flow path connecting between the first stage rotor chamber and a next stage rotor chamber of the multistage rotor chambers.

The gap between the rotor casing and the multistage rotors or the gap between the multistage rotors in each of the multistage rotor chambers downstream of the foreign material capture unit may be formed smaller than the gap therebetween upstream thereof.

This configuration can prevent foreign materials from being deposited or trapped upstream than the foreign material capture unit and allows the vacuum pump to achieve low ultimate pressure.

In addition, the vacuum pump may further comprise a pressure sensor disposed in the gas flow path upstream of the foreign material capture unit for detecting a pressure.

This configuration can measure timing of maintenance of the foreign material capture unit based on the detection of the pressure sensor.

In addition, the foreign material capture unit may comprise a reticulated or porous filter.

This configuration can suitably capture foreign materials flowing through the gas flow path.

In addition, the suction port may be connected to a chamber where a gas containing non-sublimated foreign materials occurs.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic configuration view illustrating a vacuum pump apparatus according to the present embodiment;

FIG. 2 is a schematic configuration view of the vacuum pump apparatus according to the present embodiment;

FIG. 3 is a sectional view schematically illustrating inside of a first stage rotor chamber according to the present embodiment;

FIG. 4 is a sectional view schematically illustrating inside of a second stage rotor chamber according to the present embodiment;

FIG. 5 is a schematic view illustrating an example of a foreign material capture unit;

FIG. 6 is a schematic view illustrating another example of the foreign material capture unit;

FIG. 7 is a schematic configuration view illustrating a vacuum pump apparatus according to a first modification; and

FIG. 8 is a block diagram schematically illustrating a vacuum pump apparatus according to a second modification.

DESCRIPTION OF EMBODIMENTS

FIG. 1 is a schematic configuration view illustrating a vacuum pump apparatus according to the present embodiment. FIG. 2 is a detailed configuration view of the vacuum pump apparatus according to the present embodiment. The vacuum pump apparatus according to the present embodiment is connected, for example, to a vacuum chamber (unillustrated) where CVD processing is performed and exhausts gas from the vacuum chamber. The vacuum pump apparatus according to the present embodiment can be suitably used for a vacuum chamber where a gas inside the vacuum chamber contains solid foreign materials, particularly in cases where the solid foreign materials are non-sublimated, but is not limited to this. In addition, the vacuum pump apparatus according to the present embodiment can be suitably used for a vacuum chamber where light gases such as hydrogen occur, but is not limited to this.

FIG. 1 illustrates a cross section of a vacuum pump apparatus 100 including an axial line AR1 of a pump rotor 310 of a pair of pump rotors 310 and 410. FIG. 2 illustrates a cross section of the vacuum pump apparatus 100 including axial lines AR1 and AR2 as respective rotational centers of the pair of pump rotors 310 and 410. Note that the pump rotor 310 is omitted from FIG. 1 for ease of illustration. Note also that FIG. 1 also illustrates a block diagram of a pressure sensor 620 and a control unit 700 constituting the vacuum pump apparatus 100.

As illustrated in FIGS. 1 and 2, the vacuum pump apparatus 100 includes a pair of main shafts (two rotating shafts) 300 and 400; a pair of pump rotors 310 and 410; a motor 200; a casing 500; a foreign material capture unit 600; a pressure sensor 620; and a control unit 700.

The main shafts 300 and 400 are formed extending in a direction of the axial lines AR1 and AR2, respectively. The main shafts 300 and 400 are pivotally supported to the casing 500 by bearings 302 and 402, respectively. A pair of timing gears 380 and 480 is mounted on the main shafts 300 and 400, respectively. The main shafts 300 and 400 are rotated in synchronism with power from the motor 200. The pump rotors 310 and 410 are mounted on the main shafts 300 and 400 so as to rotate integrally with rotation of the main shafts 300 and 400, respectively.

The pair of pump rotors 310 and 410 constitutes a plurality of compression stages. The pump rotor 310 includes a first stage rotor (initial stage rotor) 312, a second stage rotor (next stage rotor) 314, and a third stage rotor 316 (last stage rotor), which are mounted, spaced apart, on the main shaft 300. In addition, the pump rotor 410 includes a first stage rotor (initial stage rotor) 412, a second stage rotor (next stage rotor) 414, and a third stage rotor (last stage rotor) 416, which are mounted, spaced apart, on the main shaft 400.

The casing 500 includes a multistage rotor chamber 520, a suction port 510, an exhaust port 540, and gas flow paths 530 and 532. The casing 500 also includes a shielding portion 580 disposed between the suction port 510 and inside the first stage rotor chamber 522, namely, upstream of the first stage rotors 312 and 412.

The multistage rotor chamber 520 includes a first stage rotor chamber (initial stage rotor chamber) 522, a second stage rotor chamber (next stage rotor chamber) 524, and a third stage rotor chamber (last stage rotor chamber) 526. The first stage rotor chamber 522, the second stage rotor chamber 524, and the third stage rotor chamber 526 store the first stage rotors 312 and 412, the second stage rotors 314 and 414, and the third stage rotors 316 and 416 of the pump rotors 310 and 410, respectively. The first stage rotor chamber 522 communicates with the suction port 510 connected to a vacuum chamber (unillustrated), and the third stage rotor chamber 526 communicates with the exhaust port 540. In addition, the first stage rotor chamber 522 is connected to the second stage rotor chamber 524 through the gas flow path 530 disposed on an outer peripheral side of the rotor chamber 520. Likewise, the second stage rotor chamber 524 is connected to the third stage rotor chamber 526 through the gas flow path 532 disposed on the outer peripheral side of the rotor chamber 520. According to such a configuration, when a process gas is introduced from the suction port 510 into the first stage rotor chamber 522, then the process gas is passed through the gas flow path 530, the second stage rotor chamber 524, the gas flow path 532, the third stage rotor chamber 526, in that order, and finally exhausted outside from the exhaust port 540.

FIG. 3 is a sectional view schematically illustrating the inside of the first stage rotor chamber according to the present embodiment. FIG. 3 illustrates a cross section perpendicular to the axial lines AR1 and AR2 inside the first stage rotor chamber 522. The first stage rotors 312 and 412 are disposed to face each other inside the first stage rotor chamber 522. Minute gaps CF1 and CF2 are formed between the first stage rotors 312 and 412 and between the first stage rotors 312 and 412 and an inner surface of the casing 500, respectively. As the main shafts 300 and 400 rotate, the first stage rotors 312 and 412 rotate in opposite directions to each other to pump the gas flowed in from the suction port 510. At this time, the gas is pumped so as to pass through between the first stage rotors 312 and 412 and the inner surface of the casing 500 without passing through between the first stage rotors 312 and 412 (see bold arrows in FIG. 3).

A gas inlet to the first stage rotors 312 and 412 includes a shielding portion 580. When viewed from the suction port 510 to a gas outlet of the first stage rotor chamber 522 (viewed along a direction AD in FIG. 3), the shielding portion 580 is disposed so as to cover a gap CF1 (seal portion) between the first stage rotors 312 and 412. In other words, when viewed from the suction port 510 to the gas outlet of the first stage rotor chamber 522, the shielding portion 580 is disposed between the main shafts 300 and 400. The shielding portion 580 is preferably formed so that a boundary between the first stage rotors 312 and 412 is invisible when viewed from the suction port 510 to the gas outlet of the first stage rotor chamber 522. The shielding portion 580 may be formed integrally with the casing 500, or the shielding portion 580 may be made of materials different from those of the casing 500 and assembled into the casing 500.

The shielding portion 580 guides the gas sucked from the suction port 510 into the first stage rotor chamber 522 in a direction away from the gap CF1 between the first stage rotors 312 and 412. The materials and shape of the shielding portion 580 may be designed so as to suitably guide the gas. For example, the shielding portion 580 may be made of a tapered shaped member narrow on the upstream side and wide on the downstream or may be made of a curved surface shaped member protruding toward upstream. The thus made shielding portion 580 can prevent the gas sucked from the suction port 510 into the first stage rotor chamber 522 from directly flowing into the gap CF1 between the first stage rotors 312 and 412. If foreign materials are trapped in the gap CF1 between the first stage rotors 312 and 412 which should not be a gas passage, the first stage rotors 312 and 412 are pushed in a direction away from each other, resulting in that the first stage rotors 312 and 412 may contact the casing 500. In contrast to this, according to the present embodiment, the shielding portion 580 can prevent foreign materials from being trapped in the gap CF1 between the first stage rotors 312 and 412 and thus can improve durability of the vacuum pump apparatus 100.

FIG. 4 is a sectional view schematically illustrating the inside of the second stage rotor chamber according to the present embodiment. Note that FIG. 1 is a sectional view along line I-I of FIGS. 3 and 4. As illustrated in FIGS. 3 and 4, the second stage rotors 314 and 414 are disposed to face each other in the second stage rotor chamber 524 in the same manner as in the first stage rotor chamber 522. In addition, minute gaps CL1 and CL2 are formed between the second stage rotors 314 and 414, and between the second stage rotors 314 and 414 and the inner surface of the casing 500.

Here, according to the present embodiment, the gap CL1 between the second stage rotors 314 and 414 in the second stage rotor chamber 524 is smaller than the gap CF1 between the first stage rotors 312 and 412 in the first stage rotor chamber 522. In other words, the gap CF1 between the first stage rotors 312 and 412 is formed larger than the gap CL1 between the second stage rotors 314 and 414. The reason for this is to prevent foreign materials from being trapped in the gap CF1 between the first stage rotors 312 and 412 which should not be a gas passage in the same manner as the shielding portion 580. The reason for this is also based on findings that even a larger gap CF1 of the first stage rotor chamber 522 to be connected to the vacuum chamber little affects the performance of the vacuum pump apparatus 100. Therefore, the above described configuration can secure the performance of the vacuum pump apparatus 100 and can further prevent foreign materials from being deposited or trapped in the gap CF1 between the first stage rotors 312 and 412.

Further, according to the present embodiment, the gap CL2 between the second stage rotors 314 and 414 and the inner surface of the casing 500 in the second stage rotor chamber 524 is smaller than the gap CF2 between the first stage rotors 312 and 412 and the casing 500 in the first stage rotor chamber 522. In other words, the gap CF2 between the first stage rotors 312 and 412 and the casing 500 is formed larger than the gap CL2 between the second stage rotors 314 and 414 and the casing 500. The above described configuration can secure the performance of the vacuum pump apparatus 100 and can remarkably prevent foreign materials from being deposited or trapped in the first stage rotor chamber 522. Note that according to the present embodiment, a gap in the third stage rotor chamber 526 located downstream from the foreign material capture unit 600 is also formed smaller than the gaps CF1 and CF2 in the first stage rotor chamber 522 in the same manner as the gaps CL1 and CL2 in the second stage rotor chamber 524.

Now, refer back to FIG. 1. The foreign material capture unit 600 captures foreign materials (for example, solidified materials) contained in the process gas. As illustrated in FIG. 1, the foreign material capture unit 600 is disposed in the gas flow path 530 connecting the first stage rotor chamber 522 and the second stage rotor chamber 524. More specifically, the gas exhausted from the first stage rotor chamber 522 is passed through the foreign material capture unit 600 and flowed into the second stage rotor chamber 524.

For example, as illustrated in FIG. 5, the foreign material capture unit 600 includes a cylindrical casing 640 and a filter 650 stored in the casing 640. The filter 650 may be made of porous or reticulated materials. The filter 650 may be designed so that foreign materials contained in the process gas are suitably captured and the resistance in passing through the filter 650 is in an acceptable range. For example, the filter 650 may be made of porous materials having holes smaller than foreign materials based on the foreign materials contained in the process gas. In addition, the foreign material capture unit 600 may include a plurality of stages of filters with small resistance so as to reduce the resistance of the process gas passing therethrough. In addition, as illustrated in FIG. 6, the foreign material capture unit 600 may include a casing 640 and a plurality of filters 660 each having a hole 662. In the example illustrated in FIG. 6, the filters 660 are stored in the cylindrical casing 640 so that each hole 662 is disposed at different positions with respect to the flow direction of the process gas. In the example illustrated in FIG. 6, one hole 662 is formed for each filter 660, but two or more holes 662 may be formed. In this case, for example, each filter 660 may be stored in the cylindrical casing 640 so that each hole 662 is disposed at different positions between adjacent filters 660 with respect to the flow direction of the process gas.

The pressure sensor 620 is disposed upstream of the foreign material capture unit 600 to detect a pressure of the gas flow path 530. More specifically, the pressure sensor 620 is disposed between the first stage rotor chamber 522 and the foreign material capture unit 600. The pressure sensor 620 is configured to detect an exhaust pressure of the first stage rotor chamber 522 and a suction pressure of the foreign material capture unit 600. The pressure sensor 620 sends the detected pressure signal of the gas flow path 530 to the control unit 700.

The control unit 700 not only controls the overall operation of the vacuum pump apparatus 100 but also functions as a data storage unit 710, a data analysis unit 720, and a notification unit 730. According to the present embodiment, the control unit 700 is configured as an information processing apparatus having a CPU and a memory; and when the CPU executes programs stored in the memory, the control unit 700 performs the required functions. Note that at least some of the functions of the control unit 700 may be implemented by a dedicated hardware circuit. Note also that each function of the control unit 700 may be distributed across two or more devices.

The data storage unit 710 receives a detection signal from the pressure sensor 620 and stores the detection signal for a predetermined period of time. The data storage unit 710 stores an initial value of a pressure detected by the pressure sensor 620. The initial value is a value actually detected by the pressure sensor 620 during rated operation while the vacuum pump apparatus 100 is operating in a state in which there is no foreign material inside the foreign material capture unit 600, or at a time of replacement or maintenance of the foreign material capture unit 600. The initial value may be measured or stored before the vacuum pump apparatus 100 is shipped or after the vacuum pump apparatus 100 is installed at a location to be used (for example at a test operation). Note that the initial value may be a predesigned value.

Based on the detection signal from the pressure sensor 620, the data analysis unit 720 analyzes the deposition state of foreign materials in the foreign material capture unit 600. According to the present embodiment, the data analysis unit 720 determines whether or not a pressure detection value stored for a predetermined period of time (for example, one hour) in the data storage unit 710 is different by a predetermined degree from the initial value stored in the data storage unit 710. If a determination is made that at least one of the pressure detection values is different by the predetermined degree from the initial value, the data analysis unit 720 determines that the foreign material capture unit 600 needs to be replaced or maintained. Note that the data analysis unit 720 may use an average value instead of or in addition to an instantaneous value for analysis.

The notification unit 730 notifies of the analysis results by the data analysis unit 720. The notification may be performed by any method such that the control unit 700 itself may issue an alarm by sound or screen display or may send an alarm signal to a central control room. The user of the vacuum pump apparatus 100 can measure the timing of replacement or maintenance of the foreign material capture unit 600 based on the notification of the notification unit 730.

In the vacuum pump apparatus 100, when the motor 200 is driven, the timing gear 380 and the pump rotor 310 are rotatably driven. When the timing gears 380 and 480 are engaged with each other, the pump rotor 410 is also rotatably driven. The pair of pump rotors 310 and 410 is rotated synchronously in opposite directions in non-contact by maintaining a minute gap with the inner surface of the rotor chamber 520, and between the first stage rotors 312 and 412, between the second stage rotors 314 and 414, and between the third stage rotors 316 and 416. As the pair of pump rotors 310 and 410 rotates, the process gas introduced from the suction port 510 is pumped and sent by the first stage rotors 312 and 412, the second stage rotors 314 and 414, and the third stage rotors 316 and 416, and then is exhausted from the exhaust port 540.

According to the vacuum pump apparatus 100 of the above described present embodiment, the reticulated or porous foreign material capture unit 600 for capturing foreign materials contained in the process gas is disposed in the gas flow path 530 between the first stage rotor chamber 522 and the second stage rotor chamber 524. Thus, the foreign material capture unit 600 does not prevent suction from the vacuum chamber to the first stage rotor chamber 522. Therefore, the vacuum pump apparatus 100 can reduce the ultimate pressure inside the vacuum chamber. In addition, the foreign material capture unit 600 is disposed downstream of the first stage rotor chamber 522 whose pressure is greater than that of the suction port 510, thus allowing a simply configured foreign material capture unit 600 to be used. Furthermore, even if foreign materials are deposited in the foreign material capture unit 600, this little affects the suction of the first stage rotor chamber 522, thus reducing frequency of maintenance of the foreign material capture unit 600.

In addition, according to the vacuum pump apparatus 100 of the present embodiment, the foreign material capture unit 600 is disposed in the gas flow path 530 connecting the multistage rotor chamber 520 along the two rotating shafts. Thus, for example, a system for connecting a main pump at a subsequent stage of a booster pump can reduce the number of elements constituting the system in comparison with a system for providing the foreign material capture unit 600 between the booster pump and the main pump. Therefore, the present embodiment can provide a simplified configuration including the control system and thus can provide an inexpensive and compact configuration.

Furthermore, according to the vacuum pump apparatus 100 of the present embodiment, the pressure sensor 620 is disposed between the foreign material capture unit 600 and the first stage rotor chamber 522, and hence the timing of maintenance of the foreign material capture unit 600 can be measured based on the detection of the pressure sensor 620.

In addition, the vacuum pump apparatus 100 of the present embodiment includes the shielding portion 580 which covers the gap between the first stage rotors 312 and 412 when viewed from the suction port 510 to a gas outlet (exhaust port) of the first stage rotor chamber 522. Thus, the shielding portion 580 can prevent foreign materials from directly flowing into the gap CF1 between the first stage rotors 312 and 412 and can improve durability of the vacuum pump apparatus 100.

The vacuum pump apparatus 100 of the above embodiment has been described as a roots type vacuum pump apparatus, but may be a claw type vacuum pump apparatus. In addition, the vacuum pump apparatus 100 has been described to have three compression stages but may be a multistage vacuum pump apparatus having two or four or more compression stages, or may be a vacuum pump apparatus having a single compression stage instead of a plurality of compression stages.

The vacuum pump apparatus 100 of the above embodiment has been described to provide the foreign material capture unit 600 in the gas flow path 530 between the first stage rotor chamber 522 and the second stage rotor chamber 524. However, the foreign material capture unit 600 may be disposed in a gas flow path connecting between the stages in the multistage rotor chamber 520. For example, as illustrated by a vacuum pump apparatus 100A of a modification in FIG. 7, a foreign material capture unit 600A may be disposed in the gas flow path 532 between the second stage rotor chamber 524 and the third stage rotor chamber 526. The reason for this is based on findings that even an increase in gap upstream near the vacuum chamber between the casing 500 and the pump rotors 310 and 410 in the rotor chamber 520 or a gap between the pump rotors 310 and 410 little affects the performance of the pump apparatus 100A. Therefore, the design may be such that the foreign material capture unit 600A is disposed in the gas flow path between the stages in the multistage rotor chamber 520, and thereby foreign materials little affect the upstream side from the foreign material capture unit 600A and may secure the performance of the pump apparatus 100A on the downstream side.

The vacuum pump apparatus 100 of the above embodiment has been described, focusing on the multistage pump rotors 310 and 410 and the rotor chamber 520 along the two main shafts 300 and 400. However, the foreign material capture unit 600 may be disposed in a vacuum pump system having a plurality of compression stages for vacuum pumping the vacuum chamber. FIG. 8 is a block diagram schematically illustrating a vacuum pump system according to another modification. As illustrated in FIG. 8, a vacuum pump system 100B includes a plurality of compression stages 20 for vacuum pumping the vacuum chamber 10. The foreign material capture unit 600 is disposed in a gas flow path 40 between a first compression stage 20A and a next compression stage 20B connected to the vacuum chamber 10. Here, the first compression stage 20A may be a first pump apparatus (for example, a booster pump), and the compression stage following the next stage may be a second pump apparatus (for example, a main pump) having a plurality of compression stages. The above configuration can also exert similar effects to the above described embodiments.

The vacuum pump apparatus 100 of the above embodiment has been described such that the foreign material capture unit 600 has the reticulated or porous filter 650. However, the foreign material capture unit 600 is not limited to the above embodiment, but may have at least one of a trap and a filter. In addition, the foreign material capture unit 600 may be made of a material such as a nonwoven fabric having irregularly formed holes.

The vacuum pump apparatus 100 of the above embodiment has been described such that the control unit 700 notifies of the timing of maintenance of the foreign material capture unit 600 based on the detection signal from the pressure sensor 620, but only the detection value of the pressure sensor 620 may be stored or notified of. Alternatively, instead of providing the pressure sensor 620, the timing of maintenance of the foreign material capture unit 600 may be analyzed based on the ultimate pressure of the vacuum chamber or the like. Still alternatively, the maintenance of the foreign material capture unit 600 may be performed for each predetermined period of time.

The vacuum pump apparatus 100 of the above embodiment has been described such that the shielding portion 580 is disposed upstream of the first stage rotors 312 and 314, but the shielding portion 580 may not be disposed. In addition, the shielding portion 580 may be applied to a single stage vacuum pump apparatus. In addition, the shielding portion 580 may be disposed only between the suction port 510 and the inside of the first stage rotor chamber 522, or may be disposed upstream of the multistage rotor chamber 520, for example, as illustrated in FIG. 7. Furthermore, as illustrated in FIG. 7, the shielding portion 580 is disposed in the rotor chamber 520 located upstream from the foreign material capture unit 600 (see the shielding portions 580 and 580A), but may not be disposed in the rotor chamber 520 downstream.

The vacuum pump apparatus 100 of the above embodiment has been described such that the gap CL1 between the second stage rotors 314 and 414 is smaller than the gap CF1 between the first stage rotors 312 and 412. In addition, in the radial direction of the pump rotors 310 and 410 (in the direction perpendicular to the axial lines AR1 and AR2 of the main shafts 300 and 400), the gap CL2 between the second stage rotors 314 and 414 and the casing 500 is smaller than the gap CF2 between the first stage rotors 312 and 412 and the casing 500. However, the configuration is not limited to this embodiment. For example, the gap CL2 between the second stage rotors 314 and 414 and the casing 500 in a direction of the axial lines AR1 and AR2 of the main shafts 300 and 400 may be smaller than the gap CF2 between the first stage rotors 312 and 412 and the casing 500 (see FIG. 2). In addition, at least one of the gap CF1 between the first stage rotors 312 and 412, and the gap CF2 between the first stage rotors 312 and 412 and casing 500 may be larger than the gap CL1 between the second stage rotors 314 and 414 and the gap CL2 between the second stage rotors 314 and 414 and the casing 500. The above configuration can also exert similar effects to the vacuum pump apparatus 100 of the above embodiments.

Hereinbefore, the embodiments of the present invention have been described. The embodiments of the invention described above are intended to facilitate understanding of the present invention, but not to limit the present invention. It is readily understood that the present invention can be modified or improved without departing from the spirit thereof, and that the present invention encompasses equivalents thereof. It should be noted that within a range capable of solving at least some of the above described problems or within a range of exerting at least some of the effects, any combination of embodiments and modifications can be used and any combination of the components described in the scope of claims and the description can be used or can be omitted.

REFERENCE SIGNS LIST

-   10 vacuum chamber -   20 plurality of compression stages -   20A first compression stage -   20B next compression stage -   40 gas flow path -   100 vacuum pump -   300, 400 main shaft -   310, 410 pump rotor -   312, 412 first stage rotor -   314, 414 second stage rotor -   316, 416 third stage rotor -   500 casing -   510 suction port -   520 rotor chamber -   522 first stage rotor chamber -   524 second stage rotor chamber -   526 third stage rotor chamber -   530, 532 gas flow path -   540 exhaust port -   580 shielding portion -   600 foreign material capture unit -   620 pressure sensor -   640 casing -   650 filter -   660 filter -   662 hole -   700 control unit 

What is claimed is:
 1. A vacuum pump comprising: two rotating shafts formed extending in a first axial direction; a rotor casing including a rotor chamber disposed along the two rotating shafts, a suction port communicating with the rotor chamber, and an exhaust port communicating with the rotor chamber; rotors mounted on the two rotating shafts and disposed in the rotor chamber; and a shielding portion configured to prevent a gas sucked from the suction port into the rotor chamber from directly flowing into a gap between the rotors and disposed between the suction port and inside the rotor chamber.
 2. The vacuum pump according to claim 1, wherein the rotors are roots type rotors or claw type rotors.
 3. The vacuum pump according to claim 1, wherein when viewed from the suction port toward inside the rotor chamber, the shielding portion is disposed in front of a gap between the rotors.
 4. The vacuum pump according to claim 1, wherein the shielding portion is disposed upstream of the rotors and is disposed between the two rotating shafts when viewed from the suction port toward inside the rotor chamber.
 5. The vacuum pump according to claim 1, wherein the shielding portion has a tapered shape narrow on an upstream side and wide on a downstream side.
 6. The vacuum pump according to claim 1, wherein the shielding portion has a curved surface shape protruding toward upstream.
 7. The vacuum pump according to claim 1, wherein the rotor chamber comprises multistage rotor chambers connected to each other through a gas flow path, the rotors comprise multistage rotors, each disposed in each of the multistage rotor chambers, and the shielding portion is disposed between the suction port and inside a first stage rotor chamber of the multistage rotor chambers.
 8. The vacuum pump according to claim 7, further comprising a foreign material capture unit having at least one of a trap and a filter disposed in the gas flow path connecting between stages of the multistage rotor chambers.
 9. The vacuum pump according to claim 8, wherein the foreign material capture unit is disposed in the gas flow path connecting between the first stage rotor chamber and a next stage rotor chamber of the multistage rotor chambers.
 10. The vacuum pump according to claim 8, wherein the gap between the rotor casing and the multistage rotors or the gap between the multistage rotors in each of the multistage rotor chambers downstream of the foreign material capture unit is formed smaller than the gap therebetween upstream thereof.
 11. The vacuum pump according to claim 8, further comprising a pressure sensor disposed in the gas flow path upstream of the foreign material capture unit for detecting a pressure.
 12. The vacuum pump according to claim 8, wherein the foreign material capture unit comprises a reticulated or porous filter.
 13. The vacuum pump according to claim 1, wherein the suction port is connected to a chamber where a gas containing non-sublimated foreign materials occurs. 